This invention relates to a technique of modulating/demodulating a data in an optical recording medium.
Nowadays, an optical recording medium has been developed as a recording medium for recording various informations, such as video and audio information, etc., and has been commercially available in the market Such an optical recording medium includes a read-only type disc such as CD-ROM and DVD-ROM, etc., and a rewritable disc such as CD-R, DVD-R, CD-RW and DVD-RAM, etc.
A conventional rewritable disc modulates and demodulates a digital signal so as to stabilize an operation of a servo system upon recording of the digital signal and stabilize a reproducing clock upon reproducing thereof. Such a modulating/demodulating system for the optical recording medium has to satisfy the requirements of a high code conversion efficiency, a stable reproducing clock, an assurance of a jitter margin for a stable data detection, a small direct current (DC) component or a digital sum value (DSV) for stabilizing a data detection and a tracking servo, no error propagation or a very small error propagation and a decoding/encoding based on a small bit number for improving a recording density.
A modulating system for a CD series has adopted EFM (eight to fourteen modulation) method while a modulating system for a DVD series has adopted EFM+ (eight to fourteen modulation plus) method. By these modulating methods, a data signal with a radio frequency band is converted into a signal with a low frequency band so as to stabilize an operation of the servo system.
The EFM method converts a one-byte or 8-bit data into a 17-bit symbol data including three-bit merging words, hereinafter referred to as xe2x80x9cmodulated dataxe2x80x9d. On the other hand, the EFM+ method converts an 8-bit data into a 16-bit modulated data depending on the previous state. The modulated data is converted into a NRZI (non-return to zero inverted) code and then recorded on the optical recording medium by a mark edge method. In the data recorded on the optical recording medium in this manner, RLL (run length limited) codes, generally designated as (d, k) codes, are widely applied. Herein, d and k represent minimum and maximum run length respectively. In RLL codes, at least d xe2x80x9czerosxe2x80x9d are recorded between successive data xe2x80x9conesxe2x80x9d, and no more than k xe2x80x9czerosxe2x80x9d are recorded between successive data xe2x80x9conesxe2x80x9d. Since xe2x80x9conesxe2x80x9d at the disc means a shift, the d constraint aims at preventing intersymbol interference. The k constraint aims at making a reproducing clock by giving a sufficient shift for a data upon reproduction. For instance, in a (2, 10) codes of DVD, there are at least two xe2x80x9czerosxe2x80x9d between recorded xe2x80x9conesxe2x80x9d, and there are no more than ten recorded contiguous xe2x80x9czerosxe2x80x9d between recorded xe2x80x9conesxe2x80x9d. At this time, since a data recorded is converted into the NRZI code, a minimum time interval and a maximum time interval of the recorded data are (d+1)T and (k+1)T, respectively. Herein, T represents a channel bit interval. Accordingly, in the case of a (2, 10) code, a time interval of the data recorded on the disc exists between 3T and 11T.
Such a modulating system takes a fixed block scheme of making a one-to-one mapping of a source data into a coded data using a conversion table. To this end, the conversion table of the DVD consists of a four-set main-table in which 256 types of 16-bit code words are stored and a four-set sub-table in which 98 types of 16-bit code words from 0 to until 87 are stored. The fixed block scheme satisfies a RLL within one byte (or 8 bits), but may not satisfy a RLL between bytes, provided that there are a code rate and a RLL constraint. If a RLL is not satisfied between bytes, then one bit is added between bytes. In addition, one bit is added to minimize a DSV. Furthermore, one bit is added to satisfy a RLL again. Accordingly, if a RLL is not satisfied between bytes of the data, total three bits are added. As a result, the fixed block scheme has an advantage in the respect of a small error propagation due to the one-to-one mapping, but has a disadvantage in the respect of a limited recording capacity due to the added bits between bytes.
Meanwhile, the modulating system used for the DVD has a problem in that additional merging bits are not required since the mapping is made according to the previous state. But an encoding/decoding algorithm is complex and a large number of tables are required. A method of modulating/demodulating the present data depending on the previous data in this manner is called a look-ahead scheme. This look-ahead scheme has a low hardware complexity because an encoding/decoding algorithm is simple, and is capable of further improving a recording capacity in comparison with the fixed block scheme because only two bits of merging bits are required for a DC suppression. However, the look-ahead scheme has a drawback in that, since the present data depends on the next data or the previous data, if any one data generate an error, the next data is liable to generate an error due to such an error.
A rewritable high-density optical recording medium trends toward a code rate of ⅔ and a RLL of (1,7) or (1,8) for encoding a 8-bit source data into a 12-bit code data in order to assure a jitter margin and improve a recording capacity. In this case, a DSV must be kept at a minimum value for a stabilization of the reproduction data and the servo system.
Accordingly, it is an object of the present invention to provide a data modulating/demodulating method and apparatus for an optical recording medium that is capable of keeping a DSV at a an minimum value.
A further object of the present invention is to provide a data modulating/demodulating method and apparatus for an optical recording medium that is capable of preventing an error propagation as well as improving a recording density.
A still further object of the present invention is to provide an optical recording medium in which a data modulated by the above-mentioned modulating method has been recorded.
In order to achieve this and other objects of the invention, a data modulating method for an optical recording medium according to one aspect of the present invention includes the steps of; preparing a first set of conversion tables where a source data is converted into a coded data; preparing a second set of conversion tables for a specific source data to be converted into a coded data; converting a source data into a first and a second bit stream of coded data using both of sets of the conversion tables; calculating a digital sum value for the first and second bit streams whenever the second coded data converted from the specific source data is found; selecting the coded data stream that has smaller digital sum value; and converting the selected code data stream into a channel data stream to be recorded on the optical recording medium, wherein the code conversion rate of the conversion tables is ⅔ such that source data of a 2, 4, 6 or 8-bit data are converted into a 3, 6, 9 or 12-bit data, wherein the converted coded data stream maintains a (d, k) constraint of (1, 8), and wherein no merging bit is used between converted coded data.
A data modulating method for an optical recording medium according to another aspect of the present invention includes the step of adding a dummy bit to the source data under the (d, k) constraint to encode the source data.
A data modulating method for an optical recording medium according to still another aspect of the present invention includes the step of: preparing a set of conversion tables where a source data is converted into a coded data; converting a source data into a bit stream of coded data using the conversion tables; and converting said coded data stream into a channel data stream to be recorded on the optical recording medium, wherein the code conversion rate of the conversion tables is ⅔ such that source data of a 2, 4, 6 or 8-bit data are converted into a 3, 6, 9 or 12-bit data, wherein the converted coded data stream maintains a (d, k) constraint of (1, 8), and wherein no merging bit is used between converted coded data.
An optical recording medium according to still another aspect of the present invention is recorded with a data encoded by the above-mentioned data modulating methods.
A data demodulating method for an optical recording medium according to still another aspect of the present invention includes the steps of: detecting the channel data from the optical recording medium; preparing a first decoding table in which an decoded data corresponding to the channel data is registered; preparing a second decoding table registered with a decoded data identical to an individual coded data selected in response to a specific source data such that a digital sum value of the channel data becomes a minimum value upon encoding; and decoding the channel data detected from the optical recording medium using the first and second tables.
A data demodulating method for an optical recording medium according to still another aspect of the present invention includes the step of eliminating a dummy bit included a channel data detected from the optical recording medium upon encoding to decode the channel data.
A data modulating apparatus for an optical recording medium according to still another aspect of the present invention includes: a first set of conversion tables where a source data is converted into a coded data; a second set of conversion tables for a specific source data to be converted into a coded data; first converting means for converting a source data into a first and a second bit stream of coded data using both of sets of the conversion tables; means for calculating a digital sum value for the first and second bit streams whenever the second coded data converted from the specific source data is found; means for selecting the coded data stream that has smaller digital sum value; and second converting means for converting the selected code data stream into a channel data stream to be recorded on the optical recording medium, wherein the code conversion rate of the conversion tables is ⅔ such that source data of a 2, 4, 6 or 8-bit data are encoded into a 3, 6, 9 or 12-bit data, wherein the converted coded data stream maintains a (d, k) constraint of (1, 8), and wherein no merging bit is used between converted coded data.
A data modulating apparatus for an optical recording medium according to still another aspect of the present invention includes data encoding means for adding a dummy bit to a source data under the (d, k) constraint to encode the source data.
A data modulating apparatus for an optical recording medium according to still another aspect of the present invention includes: a set of conversion tables where a source data is converted into a coded data; first converting means for converting a source data into a bit stream of coded data using the conversion tables; and second converting means for converting the said coded data stream into a channel data stream to be recorded on the optical recording medium, wherein the code conversion rate of the conversion tables is ⅔ such that source data of a 2, 4, 6 or 8-bit data are converted into a 3, 6, 9 or 12-bit data, wherein the converted coded data stream maintains a (d, k) constraint of (1, 8), and wherein no merging bit is used between converted coded data.
An optical recording medium according to still another aspect of the present invention is recorded with a data encoded by the above-mentioned data modulating apparatuses.
A data demodulating apparatus for an optical recording medium according to still another aspect of the present invention includes: detecting means for detecting the channel data from the optical recording medium; first decoding means for decoding the channel data detected from the optical recording medium using a first decoding table in which an decoded data corresponding to the channel data is registered; and second decoding means for decoding the channel data detected from the optical recording medium using a second decoding table registered with a decoded data identical to an individual coded data selected in response to a specific source data such that a digital sum value of the channel data becomes a minimum value upon encoding.
A data demodulating apparatus for an optical recording medium according to still another aspect of the present invention includes decoding means for eliminating a dummy bit included the channel data detected from the optical recording medium upon encoding to decode the channel data.